1. Field of the Invention
The present invention relates to a manufacturing method for a semiconductor device contained in a resin-sealed semiconductor package, in particular, to a manufacturing method for a semiconductor device contained in a resin-sealed semiconductor package using a lead frame manufactured through stamping press working.
2. Description of the Related Art
Along with downsizing of mobile electronic equipment in recent years, a semiconductor package also needs to be downsized and thinned for use in such mobile electronic equipment. In the semiconductor package an encapsulated semiconductor element needs to be sealed with resin in order to protect from an environment.
Downsizing and thinning of the semiconductor package are necessary. But employment of a thick lead frame for a semiconductor package is also necessary in some application of high voltage and high current.
As a result, there has been manufactured a package in which a resin seal has a small thickness so as to suppress the thickness after sealing the semiconductor element while a lead frame having a large thickness with respect to the thickness of the resin seal is adopted. For example, there has been manufactured a pin-insertion type semiconductor package in which the resin seal has a thickness of 1.5 mm and the lead frame has a thickness of equal to or more than 0.4 mm.
Alloy 194 or other copper alloy is generally used for a material of the lead frame. Further, the lead frame is processed through etching or through press working with use of a stamping press die, and there has been proposed an invention of minimizing a gap between an island and an inner lead through etching process (see Japanese Patent Application Laid-open No. 2002-208664). The lead frame manufactured through etching process does not need preparation of a die unlike the case of the stamping press working. However, the etched lead frame requires masking with a dry film using a photoresist at the time of etching process. Since a dry film which has been used once cannot be reused, and is disposed, continuous preparation of a dry film is needed during continuous manufacturing of a lead frame. Further, since the etching process involves use of chemicals, the etching process is less accurate in obtaining a desired shape as compared to the press working with use of the stamping press die.
When the lead frame is processed with the stamping press die, the lead frame is punched with a cutter called punch. As a material of the punch, a superhard material is generally used. A characteristic of the superhard material is not only hard but also brittle. In order to avoid buckling caused by the brittleness of the superhard material, the punch for punching needs to have a width which can secure strength with respect to the lead frame to be processed. With regard to the width of the punch for punching, a minimum punching width for processing is thus determined based on a plate thickness of the lead frame. In general, when the stamping press die is used to punch a shape, the stamping press die has a punching width of equal to or larger than the plate thickness of the lead frame so as to secure the punch strength. As a result, the punch for punching a portion between the inner lead and the island also needs a width of equal to or larger than the plate thickness, with the result that a gap of at least equal to or larger than the plate thickness is needed.
Use of a thick lead frame needs reduction of the inner lead or the island in order to secure a gap of equal to or larger than the plate thickness between the inner lead and the island. The inner lead requires at least a wire connection region to which the semiconductor element is electrically connected after mounting. Further, in the semiconductor package which provides a high current, a wire electrically connecting the semiconductor element and the inner lead to each other should have a large diameter. However, reduction of the inner lead reduces the wire connection region, with the result that a target wire cannot be connected. Finally, it is required to reduce an island size. The semiconductor element on the island is generally fixed to the island with a die attach material. However, in order to secure a fixing strength between the semiconductor element and the island, the die attach material should spread to extend over a side surface of the semiconductor element to form a fillet. Accordingly, with respect to the island size, the mountable semiconductor element should have a size which enables formation of the fillet of the die attach material. That is, reduction in island size requires reduction in size of the mountable semiconductor element.
In general, the chip size of a semiconductor product increases along with addition of functions and enlargement of controllable current. As a result, reduction in island size requires reduction in size of the mountable semiconductor element, with the result that there arises a possibility that a semiconductor element having a target function cannot be mountable.
As described above, use of a thick lead frame is needed for a semiconductor package in which a high voltage and a high current should be handled. However, when the thickness of the lead frame is equal to or larger than one-fourth of the thickness of the resin seal, a flow of resin may be hindered. Such hindrance of the flow of resin may cause non-filling, in which resin is prevented from reaching a terminal end of a product, or generation of internal void, in which air is taken into the product during curing of resin, leading to degradation of reliability of the product.